Routing devices within a network, often referred to as routers, maintain tables of routing information that describe available routes through the network. Upon receiving an incoming packet, the router examines information within the packet and forwards the packet in accordance with the routing information. In order to maintain an accurate representation of the topology of the network, routers exchange routing information in accordance with a defined routing protocol, such as the Intermediate System-to-Intermediate System (IS-IS) protocol or the Open Shortest Path First (OSPF) protocol.
Multi-protocol Label Switching (MPLS) is a mechanism used to engineer traffic patterns within Internet Protocol (IP) networks. By utilizing MPLS, a source device can request a path through a network, i.e., a Label Switched Path (LSP). An LSP defines a distinct path through the network to carry MPLS packets from the source device to a destination device. A short label associated with a particular LSP is affixed to packets that travel through the network via the LSP. Routers along the path cooperatively perform MPLS operations to forward the MPLS packets along the established path. LSPs may be used for a variety of traffic engineering purposes including bandwidth management and quality of service (QoS).
A variety of protocols exist for establishing LSPs. For example, one such protocol is the label distribution protocol (LDP). Another type of protocol is a resource reservation protocol, such as the Resource Reservation Protocol with Traffic Engineering extensions (RSVP-TE). RSVP-TE uses constraint information, such as bandwidth availability, to compute and establish LSPs within a network.
Numerous types of routers exist within the Internet. Network Service Providers (NSPs), for example, maintain “edge routers” that provide Internet access to customers. These provider edge (PE) routers may also provide additional services to customers, such as supporting Virtual Private Networks (VPNs). A VPN allows an enterprise to accomplish private connectivity between site networks over a public network, such as the Internet. In general, a VPN securely connects multiple customer networks using the public network, and ensures privacy by creating “tunnels” through the public network. The tunnels may be formed by one or more LSPs.